Forensic Science: Fundamentals & Investigations, Chapter 4 1 Chapter 4 A Study of Fibers and Textiles By the end of this chapter you will be able to: identify and describe common weave patterns of textile samples compare and contrast various types of fibers through physical and chemical analysis describe principle characteristics used to identify common fibers apply forensic science techniques to analyze fibers All Rights Reserved South-Western / Cengage Learning © 2009

Forensic Science: Fundamentals & Investigations, Chapter 4 2 Introduction and How Forensic Scientists Use Fibers Fibers often fall off and are picked up during normal activities. Very small fibers easily shed from most textiles and can become trace evidence. – Direct transfer: victim  suspect or vice versa – Secondary transfer: source  suspect  victim In an investigation, collection of fibers within 24 hours is critical. – 95% of all fibers may have fallen from a victim or been lost from a scene

Forensic Science: Fundamentals & Investigations, Chapter 4 3 Introduction and How Forensic Scientists Use Fibers Fiber evaluation can show such things as: – Type of fiber – Color – Number of fibers found – Location of suspects – Point of origin – Multiple fiber transfers – Type of crime committed – Time elapsed

Forensic Science: Fundamentals & Investigations, Chapter 4 4 Sampling and Testing Fiber evidence is gathered using special vacuums, sticky tape & forceps. – Shedding from an article of clothing or a textile is the most common form of fiber transfer. Nondestructive analysis includes: – Polarizing light microscopy using special filters Natural fibers require only an ordinary microscope to find characteristic shapes and markings. – Infrared spectroscopy can reveal something of the chemical structure of other fibers that, otherwise, may look very much alike.

Forensic Science: Fundamentals & Investigations, Chapter 4 5 Sampling and Testing If a large quantity of fibers is found, some can be subjected to destructive tests such as burning them in a flame (see analysis key above) or dissolving them in various liquids. Crimes can be solved in this way by comparing fibers found on different suspects with those found at the crime scene.

Forensic Science: Fundamentals & Investigations, Chapter 4 6 Fiber Classification —Natural Fibers woven wool textile Animal fibers (made of proteins): Wool from sheep, cashmere and mohair from goats, angora from rabbits, and hair from alpacas, llamas, and camels are commonly used in textiles. Shimmering silk from caterpillar cocoons is longer and not as easily shed. –Triangular structure scatters light like a prism

Forensic Science: Fundamentals & Investigations, Chapter 4 7 Fiber Classification —Natural Fibers Plant fibers (made of the polymer cellulose): – Seeds, fruits, stems & leaves can absorb water are insoluble in water are very resistant to damage from harsh chemicals can only be dissolved by strong acids can be common at crime scenes because they become brittle over time

Forensic Science: Fundamentals & Investigations, Chapter 4 8 Fiber Classification —Natural Fibers Plant fibers: Cotton from seedpods is the plant fiber most commonly used in textiles (shown above). – Can be woven & dyed easily Coir from coconuts is durable. Hemp, jute, and flax from stems grow in bundles. – Flax is the most common, found in linen Manila and sisal from leaves deteriorate more quickly. – Manila is from abaca leaves, related to the banana tree

Forensic Science: Fundamentals & Investigations, Chapter 4 9 Fiber Classification —Natural Fibers Mineral Fibers: Fiberglass is a fibrous form of glass. Asbestos is a naturally occurring mineral with a crystalline structure. – Very durable – Pipe coverings, brake linings, ceiling tiles, floor tiles, fire- resistant work clothes, shingles, siding, insulation – When it’s broken, fibers shatter into tiny fragments that become airborne. If inhaled, they cut the lungs and scar tissue may become cancerous.

Forensic Science: Fundamentals & Investigations, Chapter 4 10 Fiber Classification —Synthetic (artificially produced) Fibers Until the nineteenth century only plant and animal fibers were used to make clothes and textiles. Half the products produced today are artificially produced. –Regenerated fibers or Polymers Polymers are monomers joined together –Artificially produced fibers include rayon, acetate, nylon, acrylics, and polyesters.

Forensic Science: Fundamentals & Investigations, Chapter 4 11 Fiber Classification —Synthetic (artificially produced) Fibers Regenerated Fibers (derived from cellulose): Rayon is the most common of this type of fiber. It can imitate natural fibers, but it is stronger. Celenese ® is cellulose chemically combined with acetate and is often found in carpets. Polyamide nylon is cellulose combined with three acetate units, is breathable, lightweight, and used in performance clothing.

Forensic Science: Fundamentals & Investigations, Chapter 4 12 Fiber Classification —Synthetic (artificially produced) Fibers Synthetic Polymer Fibers: Petroleum is the basis for these fibers, and they have very different characteristics from other fibers. –Non-cellulose Monomers in large vats are joined together to form polymers. The fibers produced are spun together into yarns. They have no internal structures, and under magnification they show regular diameters.

Forensic Science: Fundamentals & Investigations, Chapter 4 13 Fiber Classification— Synthetic (artificially produced) Fibers spandex nylon Examples of synthetic polymer fibers: Polyester—found in “polar fleece,” wrinkle-resistant, and not easily broken down by light or concentrated acid; added to natural fibers for strength. Nylon—easily broken down by light and concentrated acid; otherwise similar to polyester. Acrylic—inexpensive, tends to “ball” easily, and used as an artificial wool or fur. Olefins—high performance, quick drying, and resistant to wear.

Forensic Science: Fundamentals & Investigations, Chapter 4 14 Natural & Synthetic Comparison Man-made fibers are not damaged by microorganisms like natural fibers Man-made fibers can deteriorate in bright sunlight and melt at a lower temperature than natural fibers.

Forensic Science: Fundamentals & Investigations, Chapter 4 15 Comparison of Natural and Synthetic Fibers Visual Diagnostics of Some Common Textile Fibers under Magnification

Forensic Science: Fundamentals & Investigations, Chapter 4 16 Yarns Fibers too short in their raw state to make textiles can be spun into yarns. Weaving spun fibers (yarns) together produces clothing and many textiles.

Forensic Science: Fundamentals & Investigations, Chapter 4 17 Yarns, fabrics, and textiles Fibers can be twisted (spun) into yarn of any length, thick or thin, loose, or tight. A blend can be made to meet different needs such as resistance to wrinkling. Fibers can be woven into fabrics or textiles. – Threads are arranged side by side (the warp). – More threads (the weft) then are woven back and forth crosswise in one of a number of different patterns through the warp.

Forensic Science: Fundamentals & Investigations, Chapter 4 18 Yarns, fabrics, and textiles Weave Patterns

Forensic Science: Fundamentals & Investigations, Chapter 4 19 Plain Weave

Forensic Science: Fundamentals & Investigations, Chapter 4 20 Basket Weave

Forensic Science: Fundamentals & Investigations, Chapter 4 21 Satin Weave

Forensic Science: Fundamentals & Investigations, Chapter 4 22 Twill Weave

Forensic Science: Fundamentals & Investigations, Chapter 4 23 Leno Weave

Forensic Science: Fundamentals & Investigations, Chapter 4 24 Textiles Plain, or tabby, is the simplest weave pattern Thread count: number of threads packed together per given area – 180 – 500 count (threads per inch)

Forensic Science: Fundamentals & Investigations, Chapter Summary Summary Fibers are spun into yarns having specific characteristics. Yarns are woven, with different patterns, into clothing or textiles. Fibers, trace evidence, are a form of class evidence used by crime scene investigators. Fiber evidence may be gathered using different techniques. Fibers may be analyzed using burn tests, tests for solubility in different solutions, polarized light microscopy, or infrared spectroscopy.